Electric furnace for melting and refining metals and other materials



March 22, 1938. KELLY 2,112,161

ELECTRIC FURNACE FOR MELTING AND REFINING METALS AND OTHER MATERIALS Filed April 16, 1955 By v 6AM ATTORNEYS Patented Mar. 22, 1938 PATENT OFFICE ELECTRIC FURNACE FOR IHELTING AND BE- FINING METALS AND RIALS OTHER MATE- Thomas Daniel Kelly, Walllngton, England Application April 16, 1935, Serial No. 16,717

, In Great Britain August 15, 1934 lclaim.

This invention relates to improvements in electric furnaces using direct, alternating or induced currents, and has for its object to simplify the manufacture, greatly reduce the weight and increase the efficiency of such furnaces in both small and large sizes.

The furnace, according to this'invention is so constructed that alternating, direct or induced currents can be used therein at different stages of operation from the same supply. In order that direct current can be used for refining, in which case all impurities will go to the anode and the pure metals to the cathode, such furnaces are lined with a refractory, material which is a conductor of electricity, and the furnace is pro vided with a spout or L attachment at the side which is also lined and leads to the bottom of the furnace, and down this spout is placed an electrode which constitutes a cathode and contacts with the materials at the bottom of the furnace; so that the container for the metals or other materials is thereby made negative. The spout through which the molten material can be poured from the furnace into moulds, is also of service when it is required to add other metals, materials, air or gases to the bottom of molten metals, such an arrangement being simpler and less dangerous to operate than the ordinary type of converter now in use. The positive connection for supplying electric current to the furnace is made by means of a swinging gallows arm or other apparatus carrying a movable electrode which constitutes the anode. The are is not struck on the metals or materials but on a rel fractory electrical conducting material which protects the metals from burning or oxidizing when an arc is used and has a similar effect when used as a resistance material.

Instead of the usual very heavy refractory fire bricks and surroundings of great thickness so necessary in the ordinary electric furnace to prevent radiation of heat and to insulate the current when the furnace is hot, thin layers of ma terials may be used which are combined refractories and absolute non-conductors of electricity at all temperatures, as distinguished from the magnesia, kaolin, lime, fireclay, alundum, silica, carborundum, graphite and similar materials heretofore used and which, although considered refractory and insulators, or as having great resistance, become conductors of electricity at the high temperatures of electric furnaces and radiate most of the heat so that very often the iron casing of the furnace, which may be 18 inches I 1 to 2 it. away from the molten metal, becomes electrically alive and melts or loses its strength. An electric furnace according to the present invention therefore need not weigh any more than the usual foundry ladies. In fact ordinary ladies, and receivers, converters, or crucibles can be quickly converted by this invention into light weight electric furnaces.

Two materials which answer admirably for heat and electrical insulation are, mica and asbestos, and either of these materials or both combined may be used in very thin layers between the outer casing or reinforcement and the metal container which is in direct contact with the molten metal or other materials, thus preventing radiation of heat or electrical leakage to the outside.

To prevent the metal being oxidized or burnt by coming into contact with the arc, it is always covered with a powdered material consisting of alkaline earth chlorides and iodides, which may be cheaply obtained from sea salt, mixed with kaolin and carbon or similar materials which will make an electrically conducting layer to produce the same results. This material is always between the metal and the arc and is at the anode pole, so that all oxides and gases which rise from the molten metal, are absorbed by such material.

In order to prevent short circuiting caused by liquid metal touching theelectrodes when working with direct current, such current is usually supplied by a differentially wound generator in which the volts and amperes automatically interchange according to the load, but for this invention I find it preferable to use rectifying 35 valves of the mercury vapour, thermionic or other type, between the alternating current supply and the furnace, and thus prevent the violent fluctuations of current which are so troublesome with are furnaces. In this way the same current supply can be used all the time for supplying alternating current for melting with arc, or for heating by resistance or high or low frequency induction, and the alternating current may be changed to direct current by means of rectifying valves.

The invention thus provides an electric furnace capable of using alternating and direct current from the same supply for the same furnace at different stages of operation on the same charge, and having an intermediate lining of mica or asbestos or a mixture of these materials for electrical insulation and prevention of heat radiation, combined with an electrically conducting layer between the are (when used) and the metal or other materials being treated or melted, with a spout for the insertion or introduction of electrodes, metals or other materials to the bottom of the furnace, in most cases without disturbing the protective conducting layer on top of the metal or other material, as conditions may require. When used as a converter, the top of the metal is not covered in order that gases may escape, but when the arc is in use the metal is always covered.

The annexed drawing shows an example, more or less diagrammatic, of a furnace constructed according to my invention.

Figure l is a sectional elevation of a furnace having a spout and showing metal in the furnace and a protective conducting layer applied thereto and showing the electrodes; and

Figure 2 is a diagram of the electrical connections to the furnace.

l is the metal casing forming the body of the furnace and carrying a spout 2 positioned at an angle and leading from near the bottom of the casing I.

Inside the casing I and spout 2 is positioned a layer 3 or layers of asbestos or mica or both as an electric insulating and heat resisting material, and inside this layer 3 is positioned another layer 4 composed of ordinary refractory electrically conducting material.

5 is the metal contained within the furnace and spout, the upper part of the metal being covered with a material 6 forming an electrically conducting layer of the character hereinbefore described. I

I is the positive or anode electrode swung from a gallows arm 8, and 9 is the negative or cathode electrode positioned in the spout, with its lower end contacting with the metal 5 in the furnace.

According to the diagramFlgure 2, the furnace can be connected direct to the alternating electric current supply A. C. or connected to said current supply through a vapour or like rectitying valve II which converts the alternating current to direct current so that, by means of a double pole change over switch ll, either alternating or direct current can be used in melting the metals. I

What I do claim as my invention and desire to secure by Letters Patent is:-

In a metallurgical apparatus, a generally upright chamber having an open top and a closed bottom, said chamber being adapted to contain a layer of metal having an overlying layer of electrically conductive material, a spout operatively associated with a side of said chamber and extending downwardly toward the bottom of the latter and communicating therewith below the level of said electrically conductive layer, an anode electrode extending downwardly through the open top of said chamber into proximity to said conductive layer, and a cathode electrode extending downwardly in said spout and immersed in said metal layer and isolated from the layer of electrically conductive material in said chamber, said spout extending upwardly outside of said chamber and terminating in a pipe-like conduit having coupling means provided thereon for connecting it to a source of air or other gas under pressure, whereby an air current may be blown down said spout and upwardly through said metal layer for assisting in conveying impurities contained in the latter to said conductive layer.

THOMAS DANIEL KELLY. 

